Parallel Operation Of Two Or More Alternators; Analog Input - Pegasus GRT7-TH4 R2 Manual De Instalación, Operación Y Mantenimiento

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4.4 PARALLEL OPERATION OF TWO OR MORE ALTERNATORS

The reactive compensation method applied is called phasorial composition (see Figure 4.5). On this system, the alternator
output voltage is taken and then the composition with the alternator current is processed. The result of this interaction
introduces a sensing error in real voltage signal, causing an increase or a decrease in the alternator voltage, so maintaining
the reactive between the alternators within acceptable values. The adjustment of this compensation is made through
trimpot Drp.
According to the diagram shown above, the sensing voltage suffers an influence caused by the current coming from phase
S, which is added to voltage of phases R and T. The influence in module is small and is large in phase. This means that
there is good compensation for reactive loads and a small influence with active loads. The current transformer for reactive
compensation must be in phase S of the alternator, and the voltage feedback must be in phases R and T.
To make sure the compensation is in the correct sense, proceed as follows:
Operate the alternator in stand-alone mode (isolated from the system/grid) and apply a resistive load with about 20%
of the alternator capacity;
Then rotate the trimpot Drp completely CW. Under this condition, the alternator voltage should decrease.
Returning the trimpot completely CCW again, alternator voltage should then increase; If this occur, the CT polarity is
correct. Otherwise the CT should be reverted. This procedure is required in each machine, when several machines are
connected in parallel so as to ensure that all CT's are equally polarized. Some parallel CT characteristics are as follows:
Accuracy Class: 0,6C12,5;
Window or bar type;
Transformer current ratio will be In/5A or In/1A, where In/xA is the Current ratio primary/secondary for example: 100/5A,
150/5A, 100/1A;
Current of the secondary from 5A to regulator PAR/5 and 1A for regulator PAR/1;
The primary current of the CT must be 20% higher than the nominal current of the alternator
The working frequency of the CT must be equal to the alternator frequency;
The isolation voltage class of the CT must be higher than the output voltage of the alternator;
Should withstand 1.2 x In load.

4.5 ANALOG INPUT

The analog inputs of the GRT7-TH4 R2 AVRs have the following characteristics:
Can be –9Vcc to +9Vcc (E9) or 0Vdc to 10Vdc (E10) according to the customer specification.
They are isolated by optocouplers.
Maximum current consumption: 10mA.
16 l Automatic Voltage Regulator – GRT7-TH4 R2
Figure 4.5: Phasorial composition of the alternator